We've had issues with this as well. After lot's and lot's of monitoring and troubleshooting we actually discovered that it was a resource issue on our end. The volume that the userhome was located on had too many files for Windows to handle. How big are your LUN sizes?

Our fix was to create smaller RAID 1 set's as these have a faster read/write speed than the RAID 6 set's we had been using.